1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of handling communications of a low priority device and a machine type communication (MTC) device in a wireless communication system and related communication device.
2. Description of the Prior Art
The 3rd Generation Partnership Project (3GPP) has developed a universal mobile telecommunications system (UMTS) which adopts a wideband code division multiple access (WCDMA) as a wireless air interface. In the UMTS, a radio access network known as a universal terrestrial radio access network (UTRAN) includes multiple Node-Bs (NBs) for communicating with multiple user equipments (UEs). As a successor of a General Packet Radio Service (GPRS) system, the UMTS provides high frequency spectrum utilization, universal coverage, and high-speed multimedia data transmission which are beneficial for the UEs and the NBs of the UMTS. Please note that, the UMTS and the GPRS system can support both a packet-switch (PS) service and a circuit-switch (CS) service, while systems older than the GPRS system support only the CS service.
A long-term evolution (LTE) system supporting the 3GPP Rel-8 standard and/or the 3GPP Rel-9 standard is developed by the 3GPP as a successor of the UMTS, to further enhance performance of the UMTS to satisfy users' increasing needs. The LTE system includes a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved UTRAN (E-UTRAN) includes multiple evolved NBs (eNBs) for communicating with multiple UEs.
In above wireless communication systems, a radio access network serves as an intermediate network between a UE and a core network. That is, the UE and the core network communicate with each other via the radio access network. Further, the core network comprises a Serving GPRS Support Node (SGSN), a mobile switching center (MSC), etc. in the UMTS and the GPRS system. On the other hand, the core network comprises a serving gateway, a mobility management entity (MME), etc. in the LTE system for Non Access Stratum (NAS) control.
A machine type communication (MTC) device which can automatically perform predefined jobs and report corresponding results to other devices or servers, can be used in various areas, such as security, tracking and tracing, payment, healthcare, metering, etc. Further, the MTC device preferably reports the corresponding results via a wireless link such that limitation caused by environment is removed. However, the wireless link to be used by the MTC device is needed to be established, and resource required by the wireless link is needed to be allocated. Reuse of existing infrastructures and wireless communication systems become a viable choose for usage of the MTC device. Therefore, the GPRS system, the UMTS and the LTE system developed by the 3GPP which are widely deployed are suitable for the usage of the MTC device.
According to the prior art, a device configured as a MTC device or a low priority device can send a MTC indicator or a low priority indicator, respectively, in a signaling message (e.g. an ATTACH REQUEST or a ROUTING AREA UPDATE) to a network (e.g. a SGSN), for indicating its capability. Then, the network can configure the MTC device or the low priority device according to the received indicator. For example, the network may configure a longer periodic location update or a longer periodic routing update area timer to the MTC device or the low priority device, when the network is in congestion.
Further, when a UE performs a combined attach procedure wherein a packet switched (PS) (e.g. GPRS) attach procedure and a circuit switched (CS) (e.g. non-GPRS) attach procedure are combined with the network supporting Network Mode of Operation (NMO) I, the UE sends the MTC indicator or the low priority indicator to the network (e.g. a SGSN) in an ATTACH REQUEST Message. The network stores the indicator in a GPRS Mobility Management (GMM) context of the UE. Currently, the network does not forward the received indicator to a MSC managing the network and the UE. Hence, the MSC does not know if the UE is a low priority device or is configured as a MTC device or both. Therefore, when the MSC is in congestion, the MSC cannot prioritize the UE due to lack of related information of the UE and the resource management will not be done properly.
On the other hand, when a UE attaches for a PS (e.g. GPRS) service and a CS (e.g. non-GPRS) service and detaches only the PS service, the UE will start a periodic location update timer with a timer value received in a system information message. However, the network cannot configure a longer location update timer to the UE, when the UE detaches only the PS service. The UE will perform a periodic location update according to the periodic location update timer with the timer value received in the system information message, and flexibility for the network to configure the UE is lacked.
Besides, when a UE initiates a combined attach procedure wherein a PS (e.g. GPRS) attach procedure and a CS (e.g. non-GPRS) attach procedure are combined to a PS network (e.g. E-UTRAN or UTRAN/GERAN with NMO I) and a MSC managing the UE and the PS network is in congestion, the MSC rejects the CS attach procedure by sending a rejection cause and a back-off timer to the UE. In this situation, it is not known what the UE should do after receiving the rejection cause and the back-off timer.